We found that: (1) GGT5 is an independent prognostic gene marker for GC and can promote the tumor microenvironment; (2) GGT5 has a highly positive connection with immune-related genes, and high expression of GGT5 can alleviate the effect of ICIs on cancers; (3) GGT5 plays its role mainly by promoting memory CD8+ T cells. The gene discussed is CD8A; the disease is gastric cancer.